Hello,
I wanted to thank sirgingalot a lot, because I've tried lot of different approachs and finally it the one he provided that allowed me to do networking in 1.7.
Previously I was using FMLEventChannel which is fine and very practical but it doesn't work in MP (issue with a client-only class invoked by the FML dispatcher). I also tried the SimpleNetwork but this one throws a Netty TypeMatching exception.